(i) Field of the Invention
The present invention relates to a ceramic shell-and-tube type heat exchanger, and a method for manufacturing the same.
(ii) Description of the Related Art
Nowadays, the research and development of a forward type ceramic gas turbine have been carried out as a government project for the purposes of achieving high efficiency, low environmental pollution, the diversification of fuel, and the like. Thus, as one facet of this ceramic gas turbine, a heat exchanger made of a ceramic material having an excellent performance as a heat-resistant material for high temperatures has been developed in place of conventional metallic materials. FIG. 6 shows a schematic side view illustrating a ceramic shell-and-tube type heat exchanger which has been heretofore developed. In this drawing, two tubular plates 1a, 1b are joined and fixed to both the end portions of a plurality of heat transfer tubes 2 which are tubular ceramics, and the above-mentioned two tubular plates 1a, 1b are plate-like ceramics having a plurality of through-holes into which these heat transfer tubes 2 are inserted to be fixed.
As a method for preparing a ceramic shell-and-tube type heat exchanger, there is known a method which comprises inserting the end portions of the heat transfer tubes which are the sintered tubular ceramics into through-holes of tubular plates 1 which are unsintered plate-like ceramics having the plurality of through-holes 3 as shown in FIG. 7, and then firing these members in this condition, thereby integrally joining both the members to each other by the utilization of a difference between firing shrinkage ratios of both the members (this joining technique utilizing the difference between the firing shrinkage ratios will be hereinafter referred to as "firing join").
In this case, the firing can usually be carried out in such a condition as shown in FIG. 5 where in a sagger having a sealed structure for the purposes of preventing contamination with carbon and the like from furnace materials and of regulating an atmosphere, a setter 4 is placed, the heat transfer tubes 2 are stood on this setter 4 so as to be vertical to a floor surface, and the tubular plates 1a, 1b are positioned at both the upper and lower end portions of the tubes 2 by the use of jigs 5.
However, in the above-mentioned conventional manufacturing method, the heat transfer tubes tend to be deformed during the firing join step. Therefore, joining strength between the heat transfer tubes and the tubular plates tends to deteriorate, and gas leakage is inconveniently liable to occur owing to a joining failure between the heat transfer tubes and the tubular plates. In particular, when the heat transfer tubes are long, the stiffness of the jigs used at the time of the firing join deteriorates, so that the heat transfer tubes are further noticeably deformed, which disturbs the manufacture of the ceramic shell-and-tube type heat exchanger having long heat transfer tubes.
Furthermore, in the conventional ceramic shell-and-tube type heat exchanger, the tubular plates are joined only to both the end portions of the heat transfer tubes as described above. Therefore, in attaching the heat exchanger to the ceramic gas turbine, the heat exchanger is secured only at both the end portions thereof, and hence, at the time of the attachment, the reliability of strength and vibration resistance in a gas flow have not been sufficient.